A Methodology for Minimizing Liftgate-Induced Low-Frequency Boom Noise in Vehicles

The significance of the liftgate's role in vehicle low-frequency boom noise is highlighted by its modal coupling with the vehicle's acoustic cavity modes. The liftgate's acoustic sensitivity and susceptibility to vehicle vibration excitation are major contributors to this phenomenon. This paper presents a CAE (Computer-Aided Engineering) methodology for designing vehicle liftgates to reduce boom risk. Empirical test data commonly show a correlation between high levels of liftgate vibration response to vehicle excitations and elevated boom risk in the vehicle cabin. However, exceptions to this trend exist; some vehicles exhibit low boom risk despite high vibration responses, while others show high boom risk despite low vibration responses. These discrepancies indicate that liftgate vibratory response alone is not a definitive measure of boom risk. Nonetheless, evidence shows that establishing a vibration level control guideline during the design stage results in lower boom risk. The analysis of numerous vehicles confirms that most vehicles achieve a low forced vibration response, leading to the proposal of a vibratory response target. Furthermore, the relationship between liftgate modal coupling and the vehicle's acoustic cavity modes reveals that liftgate boom risk is a product of the liftgate's Frequency Response Function (FRF) and its acoustic sensitivity. Based on this relationship, we propose an objective target setting to minimize liftgate boom risk. Additionally, the linearity of the liftgate's response to forced vibration excitation was experimentally examined. The CAE model used in this analysis was confirmed to be accurate. The study also examines the effectiveness of the liftgate damper in reducing boom risk. This comprehensive study underscores the critical role of the liftgate in vehicle acoustics and the necessity for precise modeling to effectively mitigate low-frequency boom noise.